1. Field of the Invention
The present invention relates to an LED driving circuit and a serial LED illumination system using the same. In particular, this invention relates to an LED driving circuit and a serial LED illumination system using the same that can be operated at an AC voltage source and judges the input data signals via a comparator.
2. Description of the Related Art
As the technology that is the basis for electrical power and illumination systems has been developed, the power source for the illumination systems has become less restricted to natural power sources. Moreover, as the electronic industry has also developed, illumination methods using electrical power as the light source have become controllable. Therefore, a variety of illumination systems have been developed, including night illumination systems and decorative illumination systems having visual effects, such as neon lamps, laser lamps, and LED lamps, etc. A characteristic of decorative illumination systems is that the lamp can be patterned. Furthermore, by installing illumination lamps at the outside of a building, the outline of the building can be displayed via the light emitting from the lamps. The ensuing scene can be quite magnificent.
Recently, technological improvements have enabled LEDs to have reduced power consumption, a longer user life and add more colors to their range when used for decorative lighting displays. The LED is an illumination device in which the emitting light is visible and its bandwidth is narrow. When the diode is forward conducted, the hole carrying the carrier is combined with the electron so as to convert the potential energy into light energy. Because the LED has a low power consumption and is durable, the damage rate of its components is low. LEDs having a variety of colors have been developed. Therefore, many LEDs having a variety of colors can be composed to generate a lot of colored lights. Moreover, the light emitting from the LED is bright and stable, and its switching speed is higher than that of photogenes, so a continuous colorful imaging can be displayed. Therefore, LEDs are extensively used as lighting elements for large-sized displays, dynamic image displays or decorative illumination systems.
Reference is made to FIG. 1, which shows a circuit block diagram of an LED driving circuit of the prior art. The LED driving circuit 10 includes a shift register 102 and a driving unit 104. The shift register 102 stores the display data signals Data according to the clock signal Clock. The driving unit 104 is controlled by the data latch signal Latch and drives a full color LED to emit according to the display data signals Data stored in the shift register 102. When the shift register 102 is full, the shift register 102 outputs the display data signals that are not stored to a next LED driving circuit 10 that is connected in serial.
Reference is made to FIG. 2, which shows a block diagram of a serial LED illumination system of the prior art. The illumination system 1 is composed of a plurality of LED driving circuits 10, 12, 1n that are connected to each other in serial. The LED driving circuits 10, 12, 1n receives a DC VDD simultaneously. In the illumination system 1 of the prior art, each of the LED driving circuits 10, 12, 1n needed to receive a clock signal Clock, a display data signal Data, a data latch signal Latch, or other signals So etc.
In the illumination system 1 of the prior art, a new transmission line must be added whenever a new function is added. Therefore, the transmission lines of the illumination system become complex and it is difficult to maintain the circuit. Moreover, because each of the LED driving circuits in the illumination system 1 obtains power from the same DC VDD, the voltage in the serial LED illumination system becomes decayed. Therefore, the rear LED driving circuits can obtain a stable power from the DC VDD.